LONDON (Reuters) - Results of a trial of Pfizer’s Prevnar 7 vaccine against a major cause of pneumonia and meningitis showed on Wednesday that it can prevent three out of four cases of re-infection in HIV-infected adults in Africa.
British researchers who tested the shot in Malawi found it stopped 74 percent of recurrent cases of invasive pneumococcal disease (IPD) in patients infected with HIV, the human immunodeficiency virus that causes AIDS.
The results suggest the vaccine may benefit other high-risk adult patient groups, the researchers said, although the cost — at around $40 per dose — may pose problems in poor countries.
“This is the first trial to use a conjugate pneumococcal vaccine in an adult group and find clinical benefits,” said Neil French of the London school of Hygiene and Tropical Medicine, who led the study.
“Since it works in patients with HIV infection ... it is likely to work in other adult groups, including the elderly and other at-risk groups.”
Prevnar is a pneumococcal conjugate vaccine (PCV) designed to protect against infection with streptococcus pneumoniae bacteria, which can invade the blood stream and brain and cause invasive pneumococcal disease (IPD), in turn leading to the serious and often fatal illnesses of septicaemia and meningitis.
In HIV-infected patients, particularly in sub-Saharan Africa, the risk of developing IPD increases is between 30 and 100 times higher, the scientists said in their study in the New England Journal of Medicine.
Similar shots known as pneumococcal polysaccharide vaccines (PPVs) are currently used to protect adults in Britain and the United States, but have had limited success in HIV-infected adults and are not recommended for use in Africa.
Pfizer won approval last week for its updated version of the shot, Prevnar 13, which protects against 13 strains of streptococcus pneumoniae bacteria, as opposed to the seven tackled by the original.
The original Prevnar was introduced in 2000 and has annual sales of around $3 billion.
GlaxoSmithKline has a rival vaccine called Synflorix that acts against 10 strains, and Merck sells Pneumovax 23, which fights 23 strains and is the only vaccine of its type approved in the United States for adults.
Scientists tested the Prevnar 7 vaccine on almost 500 predominantly HIV-infected adults in Blantyre, Malawi.
Alongside their main finding, they also found the vaccine prevented disease even in HIV-infected people whose immune systems were very weak and who were starting to develop AIDS.
French described this effect as “remarkable,” and said it was probably due to the vaccine’s conjugate technology.
Polysaccharide vaccines consist of long chains of sugar molecules isolated from the infectious agent — in this case, the pneumococcal bacteria. But to boost the shot’s effect and make a conjugate vaccine, the sugar molecules can be bound to a “carrier” protein which magnifies the immune response.
“This gives hope for the possible use of conjugate technology in other vaccines targeting important HIV-associated bacterial infections,” French wrote in the study.
Editing by Greg Mahlich